Masking portions of a substrate

Abstract

A removable mask (22) protects at least one portion of a substrate (10) during treatment such as irradiation thereof. To obtain mask (22), there is applied over said portion of substrate (10) a parting layer (44) of a metal selected from the group consisting of nickel, aluminum, indium and tin. Over the parting layer (44), there is applied the removable mask (22) of a material which is adherent and harmless to the parting layer (44) and is substantially impenetrable by the treatment. After irradiation, the parting layer (44) is treated with at least a detaching agent sufficiently to detach said parting layer (44) and the mask (22) from substrate (10). For proton bombardment of a substrate (10) which includes gallium arsenide, the parting layer (44) is preferably nickel, the mask is preferably gold and the detaching agent includes hydrochloric acid.

What is claimed is: 
     
       1. A method of removably masking at least one portion of a substrate to protect said portion during irradiation of said substrate, comprising: applying over said portion, a parting layer of metal selected from the group consisting of nickel, aluminum, indium and tin, said layer being removable from the substrate by application of a detaching agent which is harmless to the substrate; and   applying over said parting layer, a masking layer of material, said material being adherent and harmless to the parting layer and being substantially impenetrable by the radiation.   
     
     
       2. A method as in claim 1, further comprising, after the irradiation is completed: treating the parting layer with at least the detaching agent sufficiently to detach said parting layer and the mask from the substrate.   
     
     
       3. A method as in claim 2, wherein the substrate includes gallium arsenide, the parting layer is nickel and the detaching agent includes hydrochloric acid. 
     
     
       4. A method as in claim 2, wherein the substrate includes gallium arsenide, the parting layer is aluminum and the detaching agent includes by volume, about 85% phosphoric acid, about 5% nitric acid, about 5% acetic acid and about 5% water. 
     
     
       5. A method as in claim 2, wherein the substrate includes gallium arsenide, the parting layer is indium and the detaching agent includes hydrochloric acid. 
     
     
       6. A method as in claim 2, wherein the substrate includes gallium arsenide, the parting layer is tin and the detaching agent includes by volume, about 98% hydrochloric acid and about 2% hydrogen peroxide. 
     
     
       7. A method as in claim 3 or 4 or 5 or 6, wherein the masking layer includes the metal gold. 
     
     
       8. A method as in clam 7, wherein irradiating the substrate includes bombarding the substrate with protons. 
     
     
       9. A method of removably applying, over at least one portion of a substrate, a gold mask to protect said portion during irradiation of said substrate, comprising: applying over said portion, a parting layer of metal selected from the group consisting of nickel, aluminum, indium and tin, said layer being removable from the substrate by application of a detaching agent which is harmless to the substrate; and   applying over said parting layer, a masking layer including the metal gold, said layer being adherent and harmless to the parting layer and being substantially impenetrable by the radiation.   
     
     
       10. A method as in claim 9, further comprising, after the substrate irradiation is completed: treating the parting layer with at least the detaching agent sufficiently to detach said layer and the gold mask from the substrate, thereby obviating a need to treat the gold mask to achieve removal thereof.